Where each NATO military power has sent forces to counter Russian aggression in the North of Europe

Experts said that Russia sees the Balkan states as part of its natural sphere of influence, and that they are determined to protect themselves from Western interference.

"Putin wants to reclaim this area," Martin Vladimirov, an analyst for the Centre for the Study of Democracy, told the Sun, even though it accepts that it is "very difficult and is probably not going to happen".

Recent research from the Bulgarian think tank said Russian investment in the region has increased by more than three billion Euros - and 13 per cent of Serbia's economy was Russian owned.

"Russia has been very good at leveraging its economic footprint in achieving political goals - through media disinformation and soft power," he said.

The country has pushed investments in energy, banking, telecommunications, and even gained close links to oligarchs and governments, in order to "achieve outside political influence".

But he said that Russia didn't actively want the countries not to join the bloc - just to continue to have influence there and stir things up.

"As long as they can undermine integration of the region within the community and leave it neutral, it appears less menacing," he added. "Russia fears encirclement."

He blasted the EU for not communicating its role in the development of the region in the last decade, and said they can only "claw" it back with a much harder push.

"The EU has been the biggest provider of foreign aid, helping businesses, and rural areas. But the people believe that Russia is the biggest investor and donor - it's been very good at channelling propaganda in the region."

Balkan states in line for EU membership - and many are joining Nato too

FIVE countries have applied formally to the EU about becoming a member.

Turkey, Serbia, Montenegro, Albania and Macedonia all want to be a part of the bloc, and all but the latter two have started accession negotiations.

Slovenia and Croatia - two other Balkan states - have already joined.

Other possible candidates include Kosovo (but the country isn't recognised by five EU states) and Bosnia and Herzegovina.

Serbia and Montenegro are expected to be accepted into the bloc by 2025 - but must negotiate the terms first, and make changes to their nations. Turkish talks are at a standstill.

Anyone who wants to be a part of the EU has to respect the principles of the bloc - liberty, democracy, freedom, human rights, the rule of law.

28 states are currently in the bloc - but that will drop down to 27 when Britain leaves in 2019.

Slovenia - member since 2004

Croatia - member since 2013

Bosnia and Herzegovina - applied in 2016

Montenegro - candidate since 2010 and negotiating

Albania - candidate since 2014

Serbia - candidate since 2012 and negotiating

Kosovo - potential candidate

Macedonia - candidate since 2005

The Nato military alliance of 27 European and two North American countries.

Seven Central and Eastern European countries: Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, and Slovenia all joined the alliance in 2004.

Albania and Croatia joined in 2009, and Montenegro joined just last year.

"This is an attractive narrative in this part of the region... the message of not wanting to be part of a European superstate, not under the umbrella of the US, we want our national sovereignty and to do our own thing," Mr Kinnock said.